The overall objective of this effort is to extend and optimize simulation software for rapid and accurate computer simulations of ultrasound therapy and imaging. This software, which will reduce the time required for time-intensive therapy and imaging simulations by at least one or two orders of magnitude relative to competing programs while simultaneously improving the accuracy achieved in the nearfield region, will allow users to quickly construct ultrasound phased array models for therapeutic and diagnostic applications and then rapidly calculate the pressure fields and images that are generated by these models. Large-scale simulations that presently take days or weeks will be completed in hours, and standard simulations will be completed in minutes. All of the most common medical ultrasound transducer geometries will be supported by this software, both for simulations of single elements and for simulations of flat and curved 1D and 2D phased arrays. The specific aims of this effort are: 1) to extend and improve fast pressure field simulations for ultrasound transducers and phased arrays driven by time-harmonic excitations, 2) to expand and enhance fast pressure field simulations for ultrasound transducers and phased arrays driven by transient excitations, and 3) to augment and optimize fast routines for simulations of phased array ultrasound imaging. Aim 1 will support the development of accelerated linear and nonlinear ultrasound simulations that are primarily intended for therapeutic applications, including HIFU (high intensity focused ultrasound). Aim 2 will support the development of rapid linear and nonlinear simulation software for transient therapeutic and diagnostic applications, and Aim 3 will support the development of fast linear and nonlinear simulations of ultrasound imaging. This centralized repository of fast, robust ultrasound simulation routines that have been thoroughly tested and debugged will facilitate rapid evaluation of ultrasound phased array systems for therapy and imaging research. The software created by this effort will address a longstanding need in the therapeutic ultrasound community for publicly available programs designed specifically for three dimensional (3D) HIFU (high intensity focused ultrasound) simulations. These programs will also address the need for better, faster simulation software for ultrasound imaging research. PUBLIC HEALTH RELEVANCE: The software created by this effort will address a longstanding need in the therapeutic ultrasound community for publicly available programs designed specifically for three dimensional (3D) HIFU (high intensity focused ultrasound) simulations. These programs will also address the need for better, faster simulation software for ultrasound imaging research. !